3 Quick Collimation Questions

[Jasonb]

Hi all...

I just got a Skywatcher Explorer 150P, which means I now have a Reflector with an adjustable primary mirror, and I have a couple of quick questions....

1. I presume if I'm going to stand the OTA on its end, I should stand it on the end that has the aperture cover on it, as otherwise I'm standing it on the primary mirror screws, which isn't a good idea?

2. Which of the screws are the adjusting screws, and which are the lock screws?

3. I kept reading 'get the collimation right, and then lightly tighten the tilt screws'. Am I wrong in thinking that if I tighten them, the adjust the tilt? Surely tightening them and loosening them adjusts the tilt, and if you get it right you leave them alone, not then tighten them?

Thanks! 

Edited March 3, 2021 by Jasonb

[johninderby]

It’s not going to bother anything if you stand the tube on the primary end or just lay it on its side.

Big headed screws are the collimation screws and small headed ones are the locking screws.

Loosen the locking screws then adjust collimation and afterwards tighten the locking screws. They should be tightened firmly. If you don’t tighten the locking screws firmly the scope will lose collimation easily. 

[Jasonb]

Thanks John!

I understand exactly what you mean about the primary mirror screws, but I should have explained, that I've read about tightening the tilt screws with regard to the secondary adjustment (in the Astrobaby guide). To my mind any adjustment on those screws moves the mirror, so I don't see how tightening them after getting it perfect doesn't just ruin it again? 

[johninderby]

The locking screws are there to lock in collimation.

After I tighten the locking screws I recheck collimation and if it has gone off a bit recollimate by adjusting the tightness of the locking screws. Sort of a secondary collimation. 

[Jiggy 67]

27 minutes ago, Jasonb said:

Thanks John!

I understand exactly what you mean about the primary mirror screws, but I should have explained, that I've read about tightening the tilt screws with regard to the secondary adjustment (in the Astrobaby guide). To my mind any adjustment on those screws moves the mirror, so I don't see how tightening them after getting it perfect doesn't just ruin it again? 

No you don’t tighten the collimation screws, they are adjustment screws, you tighten the lock screws once you’re happy with your collimation. Just tighten the lock screws hand tight and expect to collimate regularly. I always store mine upright on the primary end

[Pixies]

Hi there.

I think there's some misunderstanding. The OP was asking about tightening the secondary adjusters

33 minutes ago, Jasonb said:

I understand exactly what you mean about the primary mirror screws, but I should have explained, that I've read about tightening the tilt screws with regard to the secondary adjustment (in the Astrobaby guide). To my mind any adjustment on those screws moves the mirror, so I don't see how tightening them after getting it perfect doesn't just ruin it again? 

(as per theAstro Baby guide). To quote 'AB': 

When all three clips are in view (and some scopes may have more clips) and shown at the edge of the secondary mirror with equal space around them this part of the collimation process is complete. Tighten down the tilt adjusters and take a final check.

In my opinion, she means you should just slightly nip up the 3 adjusters (equally) to make sure it can't slip. If you do that, you will need to double-check you haven't altered the tilt. I have learnt the hard way about what damage you can do if you over-tighten them. They only need to be finger-tight.

[Tiny Clanger]

I think there's a bit of confusion creeping in here between the collimation screws (big  , primary) , the lock screws (smaller, primary) and what Jasonb refers to as the tilt screws, which I think are the ones connecting the secondary to the spider ?

Ha, beaten to it by Pixies  🙂  !

I find Gary Seronik's guide https://garyseronik.com/a-beginners-guide-to-collimation/ clearer than the astrobaby one.

[Jasonb]

Yeah, sorry, that's what I get for trying to squeeze in a couple of question while getting my daughter ready for bed!

I *think* I'm fine about the primary screws now, thanks for clarifying that, and it's also good to know that it's fine to rest the Telescope on them!

As for the secondary, yep, I think that's what's meant @Pixies, equally tightening the tilt screws a smidge to stop them slipping. the astrobaby guide calls them tilt screws, but they're basically the three allen key adjustment screws on the secondary mirror (not the main screw, which is used for adjusting the depth of the mirror in the OTA, and also the rotation of it).

I agree with you Heather, I do think the Astrobaby guide isn't always clear, it's quite long and I've tried to read it slowly bit by bit, but still get a little lost. There are some little typos in it (like referring to a pic as both a slow and fast scope example) which adds to the confusion.

I'll have a look at that other guide, thanks!

[Pixies]

2 minutes ago, Jasonb said:

some little typos in it (like referring to a pic as both a slow and fast scope example

Yep.  That threw me, too.

Also, she talks about using a Cheshire and then sets about aligning the secondary by looking at the primary clips. The whole benefit of the Cheshire is that you can avoid that by lining up the cross-hairs and the doughnut marker on the primary.

[Jasonb]

Just now, Pixies said:

Yep.  That threw me, too.

Also, she talks about using a Cheshire and then sets about aligning the secondary by looking at the primary clips. The whole benefit of the Cheshire is that you can avoid that by lining up the cross-hairs and the doughnut marker on the primary.

See, I didn't even know that! Yeah, it's a bit confusing, and I also struggle with telling the different between the Cheshire cross-hairs and the spider vanes, though I think the crosshairs tend to be blurred.

[Pixies]

Just now, Jasonb said:

though I think the crosshairs tend to be blurred.

They are with my dodgy eyes!

I reckon that if @FLO were to make or commission a series of YouTube videos on how to collimate different types of scopes with different tools, they would prove be so popular that their name would be sung throughout the heavens! Crowds of new astronomers would flock to their website and become customers for life.

[Jasonb]

Or a collimation shop you could just drop your scope off to!

[Pixies]

1 minute ago, Jasonb said:

Or a collimation shop you could just drop your scope off to!

I'll do it for a four-pack!

[Jasonb]

I live in Ireland, so I'm not sure a four-pack will cover your travel expenses!

 

[Pixies]

14 minutes ago, Jasonb said:

I live in Ireland, so I'm not sure a four-pack will cover your travel expenses!

 

Four-pack (+ expenses). Guinness is acceptable 

[Jasonb]

That said, I love Edinburgh, so maybe I'll just bring it to you!

 

[AlexK]

I'm always finalizing the collimation of the primary with locking screws all the way to not being able to move at least one of them (read: very tight).

Well. I only done that 3 times in 11 years on my z12, because after that final procedure I don't need redoing it in the field ever. It holds perfectly well (checking each time with the Star Test at ~500x) until I need to remove the cell for modding or maintenance.

I'm storing my z12 OTA in the wall closet vertically upside down to minimize dust and crawlers chances. It's secured to the dedicated transportation cradle, which is attached to the anchor bolt in the wall. 

But I have also done the Velcro mod in the cell using 9x 3M HD Velcro Dots on the cell's supporting triangles. So after resting on the retention tabs (sitting at ~0.1mm from the mirror surface in the observing position) it returns back to the collimated position ideally. You should check how your mirror is attached to the cell if at all. If not, don't store it upside down until made either a velcro dots mod or silicone tabs mod (I prefer Velcro for easy mirror removal, but it depends on the cell construction).

I would not put any stress on the cell parts even on that lightweight (in comparison) 150mm scope because the typical China-made cell is not bulletproof, neither the way it's attached to the OTA, nor the OTA material itself. Simply lowering it too fast on the hard ground may cause an immediate or hidden damage. In addition, having the primary mirror assembly so close to the many dangers of the bare ground surface in the barely balancing tall column is not safe at all. I'm always having a dedicated ground cloth at hand (full length plastic OTA cover) to safely lower the OTA down on its side if for whatever weird rare reason I cannot immediately mount it on the Dobson stool (never happened to me actually, as the OTA safety is the No.1 priority for over 40 years of the experience, thus base goes to the ground first, OTA the second).

Edited March 3, 2021 by AlexK

[John]

I used to have an Orion Optics 10 inch newtonian which had similarly projecting primary adjusting and locking screws screws. To enable it to be stood on it's mirror end I added 3 hard rubber furniture feet to the bottom of the mirror cell, spaced in between the collimation screw pairs. These feet were a bit taller than the screws projected so I could stand the scope on it's mirror end without affecting the collimation.

Over the years that I've owned newtonians of different brands I've found it best to only use the locking screws when transporting the scope in a car. Once you have the primary tilt adjusted correctly, applying the locking screws can change the collimation a little, which is annoying, so I leave them loose unless the scope is being transpored somewhere. I'm going to need to re-adjust the collimation then anyway.

 

 

 

 

 

[Jiggy 67]

Sorry @Jasonb your photo caused me think you were on about the primary collimation 

7 hours ago, John said:

applying the locking screws can change the collimation a little, which is annoying, so I leave them loose

I also leave the locking screws loose, just resting against the plate as tightening them can cause you to chase your tail trying to collimate  as John says

i’m pretty sure that storing the scope upright on the primary collimation screws would cause you to lose collimation slightly, I don’t know if there is a right or wrong way but I wouldn’t be comfortable storing it the other way up with the primary pointing downwards fighting gravity...but that’s just me.

 I collimate every time I move the scope anyway, only takes a minor adjustment of a couple of minutes with a laser

Edited March 4, 2021 by Jiggy 67

[Ricochet]

9 hours ago, Jasonb said:

Thanks John!

I understand exactly what you mean about the primary mirror screws, but I should have explained, that I've read about tightening the tilt screws with regard to the secondary adjustment (in the Astrobaby guide). To my mind any adjustment on those screws moves the mirror, so I don't see how tightening them after getting it perfect doesn't just ruin it again? 

If you tighten all the secondary screws equally the collimation should remain the same. The trick is to tighten the screws whilst looking through your Cheshire so that you can make sure the tightening locks the secondary in the correct position. Alternatively, you can just tighten the central screw which will pull the mirror stalk up against the collimation screws. 

Edit: Beaten to it by quite some time. When I opened the thread there were no visible posts about the secondary, when I hit reply lots loaded. 

Edited March 4, 2021 by Ricochet

[CraigT82]

9 hours ago, AlexK said:

I'm storing my z12 OTA in the wall closet vertically upside down to minimize dust and crawlers chances. It's secured to the dedicated transportation cradle, which is attached to the anchor bolt in the wall. 

But I have also done the Velcro mod in the cell

My god I hope you never get stopped by the police you will have some tough questions to answer

[Spile]

As well as Gary Seronak's guide mentioned above, I like Uncle Rod's guide http://uncle-rods.blogspot.com/2009/07/zen-and-art-of-telescope-collimation.html?m=1

And this video takes the same "KISS" approach...

 

[AlexK]

10 hours ago, CraigT82 said:

My god I hope you never get stopped by the police you will have some tough questions to answer

LOL! Police might stop you for much less. I've been traveling with my little red Astroscan in the backpack once and the customs officer asked me to remove it and after the thorough visual inspection demanded me to open it for further inspection... 🤯 If you don't know, the Astroscan is a well sealed all plastic telescope, even without any collimation aids:

I've barely joked out of that major ordeal.

Edited March 4, 2021 by AlexK

[Jasonb]

Thanks for all the replies everyone, I appreciate it.

I do believe I have a collimated telescope. I went with the Gary Seronik guide (thanks @Tiny Clanger!) as I found it very easy to follow. 

My Cheshire has a collimation cap built in, but when you unscrew it (so you can use it as just a cap, without the whole Cheshire tube) it's too big for the focuser tube. So I attached it to a tube from my Barlow (after removing the Barlow lens of course) and that worked perfectly. The next issue was I was finding it hard to spot the hole in the cap in the refection, so I decided to make it easier to see. I recently got some glow in the dark number stickers, so I got one of the number nines, cut off the tail, and positioned the remaining 'o' in the inside of the cap, centred around the hole.

Then, after shining a light on the sticker, when I put the cap back in, I could see the outline of the sticker glowing, and I could see it wasn't centred on the donut on the primary mirror. I loosened the locking screws on the primary, and some slow and careful adjustments got the donut in the centre of the glow in the dark sticker. I then tightened all three locking screws pretty tight, and I found that as long as I did them equally enough, the donut was still centred.

Next step in Gary's guide was looking at the secondary. I had a good look at this, but try as I might, I couldn't see any obvious issue, it all looking very centred and circular and concentric etc. etc. So I left well enough alone! Checking the donut and glow in the dark sticker were still centred, I then used the full Cheshire and I could see the crosshairs nicely centred too. So I'm calling that a success.

When I get a clear night and my mount/tripod talking to each other, I'll try a star test too to see how that looks.

So thanks for all the advice, so far I think it's worked.

[Spile]

Some have questioned Gary's method of approximately aligning the primary before the secondary but I think that he does that to ensure the primary is not way off.

He does go back to the primary.